This invention relates generally to computer disk systems. In particular, it relates to a disk controller that is adaptive to differing drives and disk media.
Computer systems very often require large amounts of storage. Magnetic disks very often supply mass storage for computer systems. Diskettes, sometimes called floppy disks, are a popular, low-cost type of magnetic disk.
As with most areas of computer technology, there has been a continuing increase in the performance of floppy disks for succeeding generations of computers. For floppy disks, increased performance is mostly measured by increased storage capacity, that is, a larger number of bits of storage on one disk. Increased disk capacity can generally be accomplished by either increasing the circumferential density or by increasing the radial density. The circumferential density, that is, the number of bits per inch of track, is usually limited by the disk media. Improved disk composition allows a greater number of magnetic domains in the same length of the track. Of course, the disk drive must be capable of reading at the higher bit rate of the improved disk media. Radial density, that is, the separation between adjacent tracks on the disks, is more strongly dependent upon the design of the disk drive and its associated reading heads. In the past, improvements to the disk system have involved an integrated upgrading of the disk drive, the disk media and the disk controller with operational parameters, such as rotational speed, optimized for the combination of the disk drive and the disk media. Although these designs have produced superior disk systems to those previously available, the improvement has presented a compatibility problem. Disks prepared by a prior generation disk system are generally not readable by the newer generation of disk system. The result is the lack of portability between the different generations of computer systems. The lack of compatibility becomes acute when the user has compiled a large stock of software on an older computer system and wishes to upgrade his computer or possibly just his disk system. He is then faced with the problem of converting his expensive software and data from the old format to the new format disk. The problem of differing disk formats may arise, not from a generational upgrading, but simply from different characteristics of disk drives from different manufacturers. For purposes of this invention, format will denote not only the arrangement of data on a disk but also the operational parameters of the drive that need to be selected to successfully access the disk. Both the disk media and the disk drive affect compatibility.
Of course, a possible solution is for the user to connect both an old style disk and a new style disk to his computer. The old style disk can be used for reading the previously generated disk and possibly writing on disks to be transported to other users who are still confined to the old style disk system. The newer disk can be used for his higher performance applications. This duplicative approach to compatibility has the obvious drawback of requiring at least two disk drives. Furthermore, in integrated computer systems, such as are being marketed in the personal computer field, the duplicative approach lacks flexibility. Some customers may have developed a large library of old style disk and would therefore require both generations of disk drives. However other customers may prefer the additional capabilities provided by the new style disks. Furthermore, the needs of a particular customer may change over time, either over a short term or a long term. While at some time the customer may want the combination of old style and new style disks, at other times, he may prefer to operate with two new style disks.
Another possible solution to the compatibility problem is to design a disk drive which can be reconfigured to read different types of disk media. Generally, this would mean that a newer style disk drive could operate in additional modes to support older style disks.
A reconfigurable disk system that accepts either differing disk drives or differing disk formats, if a particular disk drive can read and write in different formats, requires some input to the system. It is conceivable that external switches can be manually set by the user to indicate the type of disk drive or the type of disk media format. A more sophisticated, though similar approach, is for these controls to be set by the software. However, in either case, the disk user must keep track of the disk drive and the format of the particular disk currently being used. As a result, the adaptive feature of the disk system is not transparent to the user.